Fly-ash has become an important raw material for preparation of sustainable concrete. Several investigations have proved fly ash concrete to be superior than ordinary concrete, in ambient temperature, in terms of strength as well as on durability. Performances of fly ash concrete in different aggressive environment, though, are yet to be investigated. Present experimental study has been made to see the performances of such concrete at fire conditions. A newer approach of mix design of concrete has been adopted here by substituting a part of cement by fly ash weighing twice that of cement, without addition of any chemical admixture. This has made it unique from earlier works done with equal fly ash substitution for cement replaced. The book has been prepared with a brief introduction, brief description of rheology of fly ash concrete, review of literatures available on behavior of concrete at high temperatures, experimental programme, results, discussion along with a concluding remarks. The book will be helpful for the students and researchers working on properties of concrete. As well as it will help graduate students and professionals working with fly ash concrete in construction.